Much attention has been given to the development of equipment and processes to recycle fuel from fast breeder reactors and other nuclear fuel cycles. Reprocessing the fissionable material contained in irradiated core fuel subassemblies includes removing the outer metal shroud from the fuel rods and shearing the fuel rods as a bundle into short lengths. This facilitates chemical leaching of the fissionable material on the remaining metallic waste.
A typical fast breeder reactor core fuel subassembly consists of a plurality of fuel rods containing the fissionable material. Each rod is wrapped with a spacer wire and arranged into a rod bundle which is then enclosed in a hexagonal shroud. Typically, 217 of such fuel rods are bundled together with each fuel rod being approximately 6 millimeters in diameter and wrapped with a 1.5 millimeter diameter spacer wire. A typical core fuel subassembly is 426.72 centimeters in length and 11.62 centimeters in diameter. The wall thickness which has to be cut is approximately 3.448 millimeters.
Work has been underway in the development of laser cutting concepts for disassembling such nuclear fuel cores which has considered use of pulsed and low powered carbon dioxide lasers as well as high powered carbon dioxide lasers. However, the problem arises that the disassembling of the fuel rod assembly requires making a circumferential cut at one end of the shroud, a longitudinal cut to the other end of the shroud, and then a second circumferential cut. Much care must be taken in the accuracy of the cutting since the fuel rods within the shroud often become warped and are forced into direct contact with the shroud in random regions. The problem arises then of cutting the nuclear fuel rod shroud without puncturing the cladding of the interior fuel rods.
The cutting system must also be capable of reliable remote operation and maintenance due to performance in a gamma-radiation environment with possible fuel rod temperatures in the range of 260.degree. to 520.degree. C. The laser can be located outside the cell in which the cutting system and fuel core rod are enclosed.